Hygrometer



A. ALLEN HYGROMETER June 24, 1,930.

Filed Jan. 5, 1928 Patented June 24, 1930 UNITED STATES PATENT- OFFICE ALBERT ALLEN, OF WINCHESTER, .MASSACHUSETTS, ASSIGNOR TO ATLANTIC PRE CISION INSTRUMENT COMPANY, OF BOSTON, MASSACHUSETTS, A. CORPORATION 0F MASSACHUSETTS HYGROMETER Application mea January 5, 192s. erm No. 244,653.

This invention relates to hygrometers of the general typeillustrated and claimed 1n my application for patent, Serial No. 152,- 126, filed December 2, 1926, for hygrometer, i-n which is measured the moisture content of a hygrometric body held in a confined The objectl of the present invention is to associate the hygrometric body and its partial housing, acting with the sheet material to confine the body of air, in a unitary structure with' the majork portion of the circuit devices, preferably excepting only from that structure the ,secondary current measuring means which directly indicates by the position of its indicator the desired moisture content and ,departures therefrom of thematerial being tested. To this-end the various devices pertaining to the voscillatory circuits, in so far as this isdesired, are enclosed within a casing, one face of which is recessed to receive the hygrometric body, the casing being so mounted that the material to be tested is passed across this face so- 'as to substantially complete the confinement of the body of-air within the recess and about the element and causes rapid circulation of the air by the movement of the material to be tested.- One of the important advanta les of the enclosing casing lies in the fact t at it acts as a shield to protect certain of the parts, notably the high potential lead to thel moisture-.responsive element, from theu effects of machine vibration, variations in surrounding conditions, body capacity and outside electrical disturbances', to all of which it is very sensitive.

Where the moisture content of paper or other sheet material is being tested, it is preferable to form one end portion of the casing face inclined away from the sheet material to facilitate the threading of the material through the machine therepast as when starting a run or afterthe material has been broken.

For a more complete understanding of this invention, reference may be had to the accompanying drawings in which Figure 1 is a central longitudinal section through the instrument, the Wiring being omitted.

Figure 2 is an' end elevation thereof.

Figure 3 is a detail section drawnl to a larger scale than Figures 1- and 2.

Figure L1-is a wiring diagram of the circuits.

Figure 5 lis a perspective showing one manner of mounting the instrument on a machine.

' Referring to these drawings, the instruerably narrower than the casing, so that on -opposite sides thereof are portions of substantial Width across which the material, the moisture content of which is to be tested,

is passed. This casing may be mounted on the machine as shown in Figure 5. For this purpose it is shownas provided with spaced lugs 4 riding on guide bars 5 fixed to a stationary frame portion 6 of the machine,

the material to be tested, as shownLat 10,v

passing therebeneath and across the lower,

4preferably substantially Hat, face of the casing and substantially completing the coninementof albody of, air within thev; 1ecess is positioned the hygrometric member is not necessary, though it should be passed sufficiently close thereto so as to substantially confine the body of air containing the hygrometric body. This hygrometric body,

'which is preferably back of the plane of the casing face and out of contact with the material passing thereacross may be of any suitable type but as-shown it is of the type illustrated in my application hereinbefore referred to, comprising a ribbon of suitable hygrometric material such as reverted cellulose, commonly known as artificial silk.

For the purpose of minimizing the eifects of temperature change which might other- Wise have to be corrected for, the hygrometric body is preferably so mounted that its supporting portions will not change their spacing materially through the expected changes of temperature to which the instrument will be subjected. For this purpose a strip of material 19 having a substantially zero temperature coefficient of expansion,

such as 'invar steel, may be fixed at one end as at 20 within the recess 2, the other end portion being outwardly turned as at 21 and aving threaded therethrough an adjustable abutment screw 22. This abutment screw is shown as bearing against a tension rod 23 about which an end portion 24 of the ribbon vsecuring means passes, this securingpmeans being fixed as about the stationary pin 25. 'A spring 26 acts to hold the pin 23 against the end of the screw 22. c yThe securing means passes about a guide pin 27 and'i's secured to the end of the hygrometric ribbon in any suitable manner as at 28.

The opposite end of the hygrometric ribbon is shown as attached b'y any suitable means to a movable leaf 30 of a bookl condenser 31. This condenser 31 is shown in Figure 1 as positioned within a compartment 32 at one endof the recess 2 and is so near to the adjacent end ofothe strip 19 that substantially no change in ribbon length is due to'temperature change. This condenser 31 .is shown las one of the tuning elements of a secondary oscillatory circuit II (Figure 4), there being also in this circuit a variable condenser 35, which is preferably Ainitially adjusted to the desired capacity and Athen fixed, and a supplemental condenser 36 which may be varied so that the current re sponsein the secondary circuitmay `be that desired when the moisture content asdetermined by the position of the movabley leaf 30of the book condenser is at that point cor# responding to a desired moisture content of the material being tested. AvThe secondary circuit II also includes an inductance 37 and a thermocouple 38, which may'bea portion of a 'thermo-ammeter, the indicating portion ofwhich is shown at 40 and may be positioned at any desired point, preferably out- 70 side of the casing 1. The condensers and 36, the inductance 37, and Vthe thermocouple 38 are all shown in Figure 1 as carried within the casing 1. The inductance 37 vmay be a spider web coil, as shown. The high volt 75 age lead to this condenser 31 is extremely sensitive to body capacity and to any-variations in its'immediate surroundings such as might be caused by machine vibration or metal parts moving relative thereto. The 80 casting 1 acts as an effective shield for this lead, being grounded through its connection to the -machine frame. The indicating instrument 40 may bepositioned at any dev sired location, there4 being shown at 42 and 85 43 terminals on the casing to which wires may be attached leading to this instrument. The primary oscillatory circuit I by which ,current flow is induced in the secondary depending in amount on the nearness to resonance between these two circuits and the power and characteristics of the` primary circuit are also shown as carried within the casing. At is shown an inductance, which may be a spider web coil, this being in inductive relation to the coil 37, constituting the coupling between the primary and secondary oscillatory circuits. Of course any employed.

At 51 is indicated a voltmeter and at 52 -a condenser between which and the ground the voltmeter is positionedWhilc the oscil'- latory circuits may be of any suitable type, they are herein shown as of the type more fully described and claimed inthe application for patent of Robert F. Field, Serial No... 227,694, filed October 21, 1927. As'by the use of these particular circuits and choosno ing certain values of their electrical characteristics, power may betakenfromr any suitable commercial alternating current source without causing the` commercial fluc- A tuations in this voltage to have'material ef- 115 fect on tohe current lresponse inthe secondary circuit. VThe primary circuit I may-,receive its power therefore througha transformer 60, the secondary of which isldivided to provide van A battery portion 61 to light the 120 'lament 62 of a thermionic tube 65, thisf'being controlled through a rheostat V66, andfa B battery portion furnisliirigplate current for the plate 72 of thiis'tube.' Qch'oke is shown'at 73, fixed condensers at- 74, 75 and 125 v 76, and a variable resistance at 77 .i .All these parts may be positioned Withinf the casing,

Vpreferably all except the coil 50 being shieldedfrom the secondary circuit yas by the metal partition 79. At 80'is y:shown a plug 130 other suitable type 0f coupling .might be md 'eatin mechanism 40, however, preferablynbody,

bein not included within the casing in order I ,o tha itmay be' positioned at any suitable po' t which may be at a considerable dist ce` from the ca sin Of course it could included thereini desired. `In order to facilitate threading of the' 1 sheet material across the externall recessed face of the casing, it is* preferab e to provvide a shoe portion 82, herein shown as a separate piece fixed to the casing thou h ofv I course it might be formed integral i l desired, ,having one face 83 forming substantially a continuation of the recessed face .but being inclined away from the plane of this facel and away froml the adjacent surface ofthe sheet material. This acts to vpermit the ready insertion of the material through the machine and adjacent to the recessed face of the casing, it being the usual practice to so form the entering portionof the sheet that it is longer on one edge than at the 4other, this longer edge being threaded through-and drawing the remainder of the sheet with it. This longer edge should be on that side where the shoe 81 y1s positioned. Having thus described an embodiment of this invention it should be evident to those skilled inthe art that various changes and modifications might be made therein. without departing from its spiritor. scope as defined by the appended claims. .I claim:

1. An instrument of the class described comprising a metal casing having a recess in one face, a vhygrometric bod in saidrecess, primary and secondary oscil atory high frecasing, said devices including means responsive to the moisture content of saidy body quency circuit devices housedA within `said frequency circuit devices housed within said casing, said devicesincluding a variable element and means for varying said element in `response to varying moisture content of said body4 for varying the current response in said secondary circuit in accordance with variations in the 'moisture content of safd said element havingl a high potential lead in one of said circuits shielded by said cas'in and meansfor indicating such respense.

In testimony whereof I have aiiixed my signature.

' ALBERT ALLEN.-

Jforvarying the current response in said secondary circuit in accordance withvariations in the moisture content of said body, and means for indicating such res nse.

2. The combination 1n a mac 'ne for handling traveling lsheet material,v of a casing having a face across which said materia is passed, said casing having a recess in said face, a hygrometric body in said recess, mechanism includin hi h frequency cirv cuits within and shie dedy said casing and responsive to moisture conditions o f said hyg'ometric body, and means for indicating suc response.

3. An instrument of the class described comprising ametalcasing having a recess L in one'face, a hygrometric bod in said rej cess, primary and secondary oscillatory high 

